Disposable sealed capsules are known that are provided with an internal filtering element that comprise an external container or casing, made of impermeable plastic material, in the shape of a glass or cup, provided with a bottom wall and a side wall that define a cavity provided with an upper opening. The latter is closed hermetically by a cover so as to internally seal the casing the filtering element, or filter, containing the initial product from which to obtain the final product (beverage) by percolation or infusion. The cover and the bottom wall of the casing are perforable (by a suitable arrangement of the brewing machine) to enable a pressurised liquid, typically water, to be introduced, (generally from above through the cover) and the extraction of the beverage obtained by percolation or infusion (generally from the bottom, via the bottom wall).
The known capsules are made of aluminium or plastics, in the latter case by injection moulding processes or processes of thermoforming single or multilayered plastic sheets.
In one type of capsule for obtaining a final product by percolation or infusion of the initial product, the filter, which is shaped as a bag to make a respective cavity that is open upwards to contain the initial product, is fixed, in particular welded, to the side wall of the casing at an upper peripheral rim thereof that is typically in the shape of a flange. The filter divides the inside of the casing into a first upper chamber containing the product and accessible through the upper opening of the casing (to enable filling) and a second lower chamber, comprised between the filter and the bottom wall and/or the side wall of the casing, which enables the beverage obtained from the initial product to be extracted.
In known machines for making capsules for beverages, the filters are formed separately, by folding portions of suitable dimensions obtained by cutting or shearing a film of filtering material unwound from a reel. The formed filters are then inserted into and fixed to respective previously formed capsules.
The filters generally have a conical or frustoconical shape with smooth or pleated or folded walls so as to increase the passage surface of the fluid.
The known filtering elements are generally made of filter paper, a material that is permeable to liquids, light and thin that can be easily cut.